Electronic organs have been known for many years. Early electronic organs used various electro-mechanical devices for generating electrical oscillations corresponding to musical tones. Various types of electronic oscillators have been used to provide such oscillations. Some organs have used an independent oscillator for each tone. This is an expensive construction, and for cost saving reasons it has been common practice to provide twelve oscillators to provide the semitones of the top octave, and to use divide-by-two circuits to provide the tones in lower octaves. More recently it has become well known to use a single radio frequency oscillator with divider circuits of different divider ratios to produce the top octave of tones. This system is sometimes known as a top octave synthesizer (TOS). Strings of divide-by-two circuits have been used to provide the notes in lower octaves of the organ.
With the advent of reliable large scale integrated circuit (LSI) chips efforts have been made to construct electronic organs utilizing digital circuits. It is relatively easy to construct LSI chips that utilize digital circuits whereas it is relatively difficult to provide analog circuits with such LSI chips.